1. Field of the Invention
The present invention relates to ultrasonic diagnostic equipments wherein, in a mode where ultrasounds which are based on a low acoustic pressure that does not burst the bubbles of a contrast medium are transmitted when the contrast medium is given and where the intensity changes of the ultrasounds are observed, the bubbles are broken by transmitting a high acoustic pressure capable of bursting the bubbles in a moment, an index about blood flow information is estimated on the basis of the data of an echo signal group before and after the breaking of the bubbles, and the estimated information is offered to an observer.
2. Description of the Related Art
In an ultrasound contrast examination, a contrast medium which is made of shell less micro bubbles or shelled ones formed of sugar or fat is used, and a blood flow movement is observed by utilizing the enhancement of echo signals based on the contrast medium, thereby to diagnose the function of an internal organ, to differentially diagnose a tumor or to diagnose the degree of progression of the tumor, or to follow up a therapeutic effect. Contrast media which are currently permitted to be injected into blood from veins for the purpose of ultrasonic diagnoses, within the State of Japan, are of the property of generating intense signals when the contrast media are caused to collapse and disappear by ultrasound transmission. The contrast medium of this property can produce a greater contrasting effect by positively breaking bubbles. However, each time the bubbles are broken for imaging, the contrasting effect is shortened. It is therefore impossible to observe intensity changes repeatedly with one time of contrast medium injection. The contrast medium must be sometimes injected anew, depending upon the contents of the diagnosis. When the quantity of injection increases in this manner, a patient is forced to bear a physical burden and an economical burden correspondingly.
Meanwhile, in recent years, bubbles which generate intense nonlinear signals without being broken by low-acoustic-pressure ultrasounds have been developed as ultrasound contrast media of next generation (hereinbelow, also termed “next-generation contrast media”). The next-generation contrast medium presents the enhancement of the signals under a low acoustic pressure without causing the bubbles to collapse and disappear as in the conventional contrast medium, so that it permits a region of interest to be repeatedly diagnosed. Incidentally, at present, the next-generation contrast media are at the stage of clinical drug trials within the State of Japan. In contrast, they have already been authorized and employed at clinical sites in some oversea regions.
Most suited as an imaging method which employs the bubbles of such a next-generation contrast medium is a technique which does not directly apply the conventional method of causing the bubbles to collapse by transmitting ultrasounds under the high acoustic pressure, but which transmits the ultrasounds under a low acoustic pressure that does not cause the bubbles to collapse, and which utilizes the reflected waves of the transmitted ultrasounds. The manufacturers of ultrasonic diagnostic equipments have developed equipments capable of coping with the next-generation contrast media, and have already put these equipments into the market.
On the other hand, as an imaging technique employing the ultrasound contrast medium has been established in recent years, it has been vigorously attempted to offer, not only an image requiring a subjective judgment for a diagnosis, but also objective quantitative information. The “objective quantitative information” is, for example, that quantitative information on a blood flow which is obtained from the changes of signal enhancement versus time as are based on the contrast medium. Owing to such quantitative information, it is possible to make the diagnosis of the function of an internal organ or the differential diagnosis of a tumor and the diagnosis of the degree of progression of the tumor more objectively.
When the quantitative information is to be acquired using the conventional ultrasound contrast medium (which is not of the next generation), high-acoustic-pressure ultrasounds (ultrasounds for imaging) need to be transmitted a plurality of times with transmission intervals changed. Ultrasound scans are performed many times at the different transmission intervals in this manner, for the following reason: as already stated, the micro bubbles forming the conventional ultrasound contrast medium are caused to collapse and disappear by the transmission of the high-acoustic-pressure ultrasounds for imaging, and the bubbles (the contrast medium) within a scanning plane are broken by each time of transmission. In order to collect data corresponding to various elapsed times, therefore, ultrasound transmission operations in which the respective time periods are individually caused to lapse are required. In a case, for example, where the data of a TIC (Time Intensity Curve) till 20 seconds sampled and collected at time intervals of one second, a time period of 1+2+3+ . . . +18+19+20=210 seconds is expended.
FIG. 11A is a diagram showing a scan sequence example in the case where high-acoustic-pressure ultrasounds are transmitted with transmission intervals changed. Echo signals obtained by ultrasound transmission conforming to the sequence are plotted in correspondence with the respective time intervals as shown in FIG. 11B. A function thus found becomes a curve (time intensity curve) indicative of a state where a contrast medium is accumulated with the lapse of time. A doctor can obtain objective quantitative information on the basis of the curve.
However, problems as stated below by way of example are involved in acquiring the objective quantitative information with the ultrasound contrast medium.
In the first place, operator such as a doctor must continue to hold an identical section during the intermittent transmission with the time intervals changed. This is difficult due to the motions of internal organs in a scanning mode, and from a technical viewpoint.
Secondly, breath holding for a long time period (which is generally said to be about 10-15 seconds though opinions differ depending upon doctors and technicians) must be required of a patient in order to suppress the organic motions in, for example, the abdominal region. This becomes a heavy burden particularly on the elderly, patients of low physical strengths, and others.
Thirdly, in a case where the section of data acquired at the different time intervals has shifted due to a two-dimensional or three-dimensional movement, the reliability of the quantitative information lowers.
Incidentally, as disclosed in, for example, JP-A-2003-61959, a scanning time period in such problems involved in the acquisition of the quantitative information can be shortened to a certain degree by contriving the scan sequence of the high-acoustic-pressure ultrasounds. From the viewpoint of lightening the burdens on the operator and the person to-be-photographed, however, it is desired to shorten the scanning time period still further.